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Over 70% of diffuse intrinsic pediatric gliomas, an aggressive brainstem tumor, harbor heterozygous mutations that create a K27M amino acid substitution (methionine replaces lysine 27) in the tail of histone H3.3. The role of the H3.3K27M mutation in tumorigenesis is not fully understood. Here, we use a human embryonic stem cell system to model this tumor. We show that H3.3K27M expression synergizes with p53 loss and PDGFRA activation in neural progenitor cells derived from human embryonic stem cells, resulting in neoplastic transformation. Genome-wide analyses indicate a resetting of the transformed precursors to a developmentally more primitive stem cell state, with evidence of major modifications of histone marks at several master regulator genes. Drug screening assays identified a compound targeting the protein menin as an inhibitor of tumor cell growth in vitro and in mice.

An in vitro model to study the early events that direct human embryo development after formation of the blastocyst and implantation in the uterine wall. Early-stage human embryo model Ali Brivanlou and colleagues have established an in vitro model to study the events that direct human embryo development between the formation of the blastocyst and implantation in the womb. They delineate key species-specific events during epiblast expansion, lineage segregation, trophoblast specification, bi-laminar disc formation and yolk sac cavitation. Implantation of the blastocyst is a developmental milestone in mammalian embryonic development. At this time, a coordinated program of lineage diversification, cell-fate specification, and morphogenetic movements establishes the generation of extra-embryonic tissues and the embryo proper, and determines the conditions for successful pregnancy and gastrulation. Despite its basic and clinical importance, this process remains mysterious in humans. Here we report the use of a novel in vitro system 1 , 2 to study the post-implantation development of the human embryo. We unveil the self-organizing abilities and autonomy of in vitro attached human embryos. We find human-specific molecular signatures of early cell lineage, timing, and architecture. Embryos display key landmarks of normal development, including epiblast expansion, lineage segregation, bi-laminar disc formation, amniotic and yolk sac cavitation, and trophoblast diversification. Our findings highlight the species-specificity of these developmental events and provide a new understanding of early human embryonic development beyond the blastocyst stage. In addition, our study establishes a new model system relevant to early human pregnancy loss. Finally, our work will also assist in the rational design of differentiation protocols of human embryonic stem cells to specific cell types for disease modelling and cell replacement therapy.

Our recent perplexing findings that polyploid giant cancer cells (PGCCs) acquired embryonic-like stemness and were capable of tumor initiation raised two important unanswered questions: how do PGCCs acquire such stemness, and to which stage of normal development do PGCCs correspond. Intriguingly, formation of giant cells due to failed mitosis/cytokinesis is common in the blastomere stage of the preimplantation embryo. However, the relationship between PGCCs and giant blastomeres has never been studied. Here, we tracked the fate of single PGCCs following paclitaxel-induced mitotic failure. Morphologically, early spheroids derived from PGCCs were indistinguishable from human embryos at the blastomere, polyploid blastomere, compaction, morula and blastocyst-like stages by light, scanning electron or three-dimensional confocal scanning microscopy. Formation of PGCCs was associated with activation of senescence, while budding of daughter cells was associated with senescence escape. PGCCs showed time- and space-dependent activation of expression of the embryonic stem cell markers OCT4, NANOG, SOX2 and SSEA1 and lacked expression of Xist. PGCCs acquired mesenchymal phenotype and were capable of differentiation into all three germ layers in vitro . The embryonic-like stemness of PGCCs was associated with nuclear accumulation of YAP, a key mediator of the Hippo pathway. Spheroids derived from single PGCCs grew into a wide spectrum of human neoplasms, including germ cell tumors, high-grade and low-grade carcinomas and benign tissues. Daughter cells derived from PGCCs showed attenuated capacity for invasion and increased resistance to paclitaxel. We also observed formation of PGCCs and dedifferentiation in ovarian cancer specimens from patients treated with chemotherapy. Taken together, our findings demonstrate that PGCCs represent somatic equivalents of blastomeres, the most primitive cancer stem cells reported to date. Thus, our studies reveal an evolutionarily conserved archaic embryonic program in somatic cells that can be de-repressed for oncogenesis. Our work offers a new paradigm for cancer origin and disease relapse.

Retinoblastoma (Rb) is the most prevalent intraocular malignancy in children, with a worldwide survival rate <30%. We have developed a cancerous model of Rb in retinal organoids derived from genetically engineered human embryonic stem cells (hESCs) with a biallelic mutagenesis of the RB1 gene. These organoid Rbs exhibit properties highly consistent with Rb tumorigenesis, transcriptome, and genome-wide methylation. Single-cell sequencing analysis suggests that Rb originated from ARR3-positive maturing cone precursors during development, which was further validated by immunostaining. Notably, we found that the PI3K-Akt pathway was aberrantly deregulated and its activator spleen tyrosine kinase (SYK) was significantly up-regulated. In addition, SYK inhibitors led to remarkable cell apoptosis in cancerous organoids. In conclusion, we have established an organoid Rbmodel derived from genetically engineered hESCs in a dish that has enabled us to trace the cell of origin and to test novel candidate therapeutic agents for human Rb, shedding light on the development and therapeutics of other malignancies.

Photoreceptor degeneration due to retinitis pigmentosa (RP) is a primary cause of inherited retinal blindness. Photoreceptor cell-replacement may hold the potential for repair in a completely degenerate retina by reinstating light sensitive cells to form connections that relay information to downstream retinal layers. This study assessed the therapeutic potential of photoreceptor progenitors derived from human embryonic and induced pluripotent stem cells (ESCs and iPSCs) using a protocol that is suitable for future clinical trials. ESCs and iPSCs were cultured in four specific stages under defined conditions, resulting in generation of a near-homogeneous population of photoreceptor-like progenitors. Following transplantation into mice with end-stage retinal degeneration, these cells differentiated into photoreceptors and formed a cell layer connected with host retinal neurons. Visual function was partially restored in treated animals, as evidenced by two visual behavioral tests. Furthermore, the magnitude of functional improvement was positively correlated with the number of engrafted cells. Similar efficacy was observed using either ESCs or iPSCs as source material. These data validate the potential of human pluripotent stem cells for photoreceptor replacement therapies aimed at photoreceptor regeneration in retinal disease.

Investigation of neural cells from post-mortem human brains and differentiated from patient-derived induced pluripotent stem cells shows that the LRRK2 mutation (G2019S) associated with familial and sporadic Parkinson's disease correlates with abnormalities at the nuclear envelope. Cell nucleus abnormalities in Parkinson's disease The G2019S mutation in leucine-rich repeat kinase 2 (LRRK2) is associated with familial and sporadic Parkinson's disease, but the pathological mechanism involved is unclear. Here, Juan Carlos Izpisua Belmonte and colleagues report that neurons bearing the LRRK2 (G2019S) mutation have profound abnormalities at the nuclear envelope. The authors validate this finding in neurons differentiated from patient-derived induced pluripotent stem cells, as well as in neurons from postmortem brains. These findings associate the nucleus with Parkinson's disease pathology, and have implications for diagnosis and the potential development of targeted therapeutics. Nuclear-architecture defects have been shown to correlate with the manifestation of a number of human diseases as well as ageing 1 , 2 , 3 , 4 . It is therefore plausible that diseases whose manifestations correlate with ageing might be connected to the appearance of nuclear aberrations over time. We decided to evaluate nuclear organization in the context of ageing-associated disorders by focusing on a leucine-rich repeat kinase 2 ( LRRK2 ) dominant mutation (G2019S; glycine-to-serine substitution at amino acid 2019), which is associated with familial and sporadic Parkinson’s disease as well as impairment of adult neurogenesis in mice 5 . Here we report on the generation of induced pluripotent stem cells (iPSCs) derived from Parkinson’s disease patients and the implications of LRRK2 (G2019S) mutation in human neural-stem-cell (NSC) populations. Mutant NSCs showed increased susceptibility to proteasomal stress as well as passage-dependent deficiencies in nuclear-envelope organization, clonal expansion and neuronal differentiation. Disease phenotypes were rescued by targeted correction of the LRRK2 (G2019S) mutation with its wild-type counterpart in Parkinson’s disease iPSCs and were recapitulated after targeted knock-in of the LRRK2 (G2019S) mutation in human embryonic stem cells. Analysis of human brain tissue showed nuclear-envelope impairment in clinically diagnosed Parkinson’s disease patients. Together, our results identify the nucleus as a previously unknown cellular organelle in Parkinson’s disease pathology and may help to open new avenues for Parkinson’s disease diagnoses as well as for the potential development of therapeutics targeting this fundamental cell structure.

Neonatal diabetes is caused by single gene mutations reducing pancreatic β cell number or impairing β cell function. Understanding the genetic basis of rare diabetes subtypes highlights fundamental biological processes in β cells. We identified 6 patients from 5 families with homozygous mutations in the YIPF5 gene, which is involved in trafficking between the endoplasmic reticulum (ER) and the Golgi. All patients had neonatal/early-onset diabetes, severe microcephaly, and epilepsy. YIPF5 is expressed during human brain development, in adult brain and pancreatic islets. We used 3 human β cell models (YIPF5 silencing in EndoC-βH1 cells, YIPF5 knockout and mutation knockin in embryonic stem cells, and patient-derived induced pluripotent stem cells) to investigate the mechanism through which YIPF5 loss of function affects β cells. Loss of YIPF5 function in stem cell-derived islet cells resulted in proinsulin retention in the ER, marked ER stress, and β cell failure. Partial YIPF5 silencing in EndoC-βH1 cells and a patient mutation in stem cells increased the β cell sensitivity to ER stress-induced apoptosis. We report recessive YIPF5 mutations as the genetic cause of a congenital syndrome of microcephaly, epilepsy, and neonatal/early-onset diabetes, highlighting a critical role of YIPF5 in β cells and neurons. We believe this is the first report of mutations disrupting the ER-to-Golgi trafficking, resulting in diabetes.

Key Points Human embryonic stem cells (HESCs) share cellular and molecular phenotypes with tumour cells and cancer cell lines. When injected into immunodeficient mice, HESCs form teratomas. The tumorigenicity of HESCs is a major hurdle, which must be confronted before the achievements from this field of research can be safely translated into the clinic. Sharing with HESCs their basic properties of self-renewal and pluripotency, human induced pluripotent stem cells (HiPSCs) also share their tumorigenic traits. However, HESCs and HiPSCs are not identical, and a rapidly accumulating body of work suggests considerable differences between these two pluripotent cell types. The transcription factors commonly used for reprogramming somatic cells into HiPSCs ( OCT4 , SOX2 , MYC and krupple-like factor 4 ( KLF4 )) are highly expressed in various types of cancer. HiPSCs are commonly derived using integrating vectors, thus creating a risk for genetic alterations and for reactivation of the reprogramming factors at later stages. HiPSCs can acquire chromosomal aberrations, even more readily than HESCs. These can result from their somatic cells of origin, reprogramming stress and during culture adaptation. Aneuploidy of pluripotent stem cells has been suggested to increase their tumorigenicity. Epigenetic differences between HESCs and HiPSCs also affect their tumorigenicity. The reprogramming process is often accompanied by epigenetic alterations. The epigenetic 'memory' of the cells might also contribute to their tumorigenicity. Self-renewal is important for the tumorigenic traits of HESCs and HiPSCs, and cell cycle-related genes are crucial for an efficient reprogramming process. These genes are also involved in the genomic instability that characterizes pluripotent cells. Owing to genetic and epigenetic causes, HiPSCs are more tumorigenic than HESCs, and harbour a risk for the development of teratocarcinomas and possibly somatic tumours. In order to develop safe HESC- and HiPSC-based treatments, the tumorigenicity hurdle must be overcome. Three general strategies to cope with this risk have been suggested: terminal differentiation or complete elimination of residual pluripotent stem cells from culture; interfering with tumour-progression genes to prevent tumour formation from the residual pluripotent cells; and tumour detection and elimination after its initial formation in the patient's body. The unique ability of human pluripotent stem cells to self-renew and to differentiate into cells of the three germ layers makes them an invaluable tool for the future of regenerative medicine and tumorigenic research. It was assumed that human induced pluripotent stem cells (HiPSCs) would behave like their embryonic counterparts in respect to their tumorigenicity, but a rapidly accumulating body of evidence suggests that there are important differences. The unique abilities of human pluripotent stem cells to self-renew and to differentiate into cells of the three germ layers make them an invaluable tool for the future of regenerative medicine. However, the same properties also make them tumorigenic, and therefore hinder their clinical application. Hence, the tumorigenicity of human embryonic stem cells (HESCs) has been extensively studied. Until recently, it was assumed that human induced pluripotent stem cells (HiPSCs) would behave like their embryonic counterparts in respect to their tumorigenicity. However, a rapidly accumulating body of evidence suggests that there are important genetic and epigenetic differences between these two cell types, which seem to influence their tumorigenicity.

The spliceosome is a critical cellular machinery responsible for pre-mRNA splicing that is essential for the proper expression of genes. Mutations in its core components are increasingly linked to neurodevelopmental disorders, such as primary microcephaly. Here, we investigated the role of SNW domain–containing protein 1 (SNW1), a spliceosomal protein, in splicing integrity and neurodevelopment. We identified 9 heterozygous mutations in the SNW1 gene in patients presenting with primary microcephaly. These mutations impaired SNW1’s interactions with core spliceosomal proteins, leading to defective RNA splicing and reduced protein functionality. Using Drosophila melanogaster and human embryonic stem cell–derived cerebral organoids models, we demonstrated that SNW1 depletion resulted in significant reductions in neural stem cell proliferation and increased apoptosis. RNA-Seq revealed disrupted alternative splicing, especially skipping exons, and altered expression of neurodevelopment-associated genes ( CENPE , MEF2C , and NRXN2 ). Our findings provide crucial insights into the molecular mechanisms by which SNW1 dysfunction contributes to neurodevelopmental disorders and underscore the importance of proper spliceosome function in brain development.

The proliferation, differentiation and survival of mononuclear phagocytes depend on signals from the receptor for macrophage colony-stimulating factor, CSF1R. The mammalian Csf1r locus contains a highly conserved super-enhancer, the fms -intronic regulatory element (FIRE). Here we show that genomic deletion of FIRE in mice selectively impacts CSF1R expression and tissue macrophage development in specific tissues. Deletion of FIRE ablates macrophage development from murine embryonic stem cells. Csf1r ΔFIRE/ΔFIRE mice lack macrophages in the embryo, brain microglia and resident macrophages in the skin, kidney, heart and peritoneum. The homeostasis of other macrophage populations and monocytes is unaffected, but monocytes and their progenitors in bone marrow lack surface CSF1R. Finally, Csf1r ΔFIRE/ΔFIRE mice are healthy and fertile without the growth, neurological or developmental abnormalities reported in Csf1r −/− rodents. Csf1r ΔFIRE/ΔFIRE mice thus provide a model to explore the homeostatic, physiological and immunological functions of tissue-specific macrophage populations in adult animals. The lineage-specific receptor CSF1R controls macrophage development and homeostasis. Here the authors show that deletion of a conserved Csf1r enhancer (FIRE) selectively depletes brain microglia and resident macrophages in the epidermis, kidney, heart and peritoneum of otherwise healthy mice.